Mask Effectiveness

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   Hi, 

I just found an interesting article regarding mask effectiveness.  This article appeared in the Canadian Medical Association's Journal.  While not specifically addressing avian influenza, it talks about particle size and why one "N" number is better than another in relation to SARS.  I thought you might find it interesting.

Here is the text:

The best protection 
John H. Lange 
Environmental and Occupational Health Consultant, Envirosafe Training and Consultants, Inc., Pittsburgh, Pa. 

The transmission of the virus causing severe acute respiratorysyndrome (SARS) appears to be by aerosol droplet and possiblythrough other routes.¹ Therefore, it is recommended that healthcare workers and others who may be exposed¹ employ respiratoryand other personal protective equipment.^2,3 The type of respiratorthat has typically been used by health care workers is the N95half-mask.^2,3 As correctly stated by Richard Schabas,² the "N95-ratedmask" is 95% filtration efficient,⁴ but does this level of efficiencyprovide the best protection for those at risk of exposure? Theeffectiveness of the N95 respirator has been supported by asmall study on prevention of occupational transmission of infection.¹However, for work with bacterial bioaerosols and chemical andbiological warfare agents, some have suggested that N95 masksare inappropriate^5,6 because these respirators do not provide"absorbent capability" and because of the amount of mask leakage,which can be about 5% through the filter and 10% around themask,⁷ even if properly fitted. For biological diseases likeSARS, for which just a few particles may be sufficient for infection,the N95 mask may indeed be inadequate, and some health careworkers may therefore become infected even if they use the respiratorproperly.

A better selection for respiratory protection would be an N100respirator with an ultra-low penetrating air filter (ULPA),which would cost only slightly more than an N95 respirator.N100 respirators have an efficiency of 99.977%,⁸ and ULPA filtersare 99.999% efficient for monodispersed particles 0.12 �min diameter or larger.⁹ HEPA (high-efficiency particulate air)filters would not be the best selection for use with a respiratorbecause their efficiency is 99.97% for monodispersed particles0.3 �m in diameter or larger, and coronaviruses are smallerthan this (at about 60 to 200 nm). For effective operation ofan N100 respirator with ULPA, the user must be fit-tested. TheUnited States and many other countries have numerous requirementsfor using a negative-pressure air-purifying respirator, includingmedical evaluation and training, as well as yearly fit-testing.

John H. Lange Environmental and Occupational Health ConsultantEnvirosafe Training and Consultants, Inc. Pittsburgh, Pa.
References 
1.  Seto WH, Tsang D, Yung RWH, Ching TY, Ng TK, Ho M, et al. Effectiveness of precautions against droplets and contact in prevention of nosocomial transmission of severe acute respiratory syndrome (SARS). Lancet 2003;361:1519-20.[Medline] 
2.  Schabas R SARS: prudence, not panic [editorial]. CMAJ 2003;168:1232-33. [Free Full Text] 
3.  Centers for Disease Control. Update: severe acute respiratory syndrome � United States, 2003. MMWR Morbid Mortal Wkly Rep 2003;52: 357-60. [Medline] 
4.  Martyny J, Glazer CS, Newman LS. Respiratory protection. N Engl J Med2002;347:824-30. [Free Full Text] 
Sawicki J. Protection from chemical and biological warfare. Surg Serv Manage 1999;5(Sep):11. Available: 

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Guests Members Profile Send Private Message Find Members Posts Add to Buddy List Guest Group	Post Options Post Reply Quote Guests Thanks(0) Quote Reply Topic: Mask Effectiveness Posted: May 30 2006 at 6:17pm
	Hi, I just found an interesting article regarding mask effectiveness. This article appeared in the Canadian Medical Association's Journal. While not specifically addressing avian influenza, it talks about particle size and why one "N" number is better than another in relation to SARS. I thought you might find it interesting. Here is the text: The best protection John H. Lange Environmental and Occupational Health Consultant, Envirosafe Training and Consultants, Inc., Pittsburgh, Pa. The transmission of the virus causing severe acute respiratorysyndrome (SARS) appears to be by aerosol droplet and possiblythrough other routes.¹ Therefore, it is recommended that healthcare workers and others who may be exposed¹ employ respiratoryand other personal protective equipment.^2,3 The type of respiratorthat has typically been used by health care workers is the N95half-mask.^2,3 As correctly stated by Richard Schabas,² the "N95-ratedmask" is 95% filtration efficient,⁴ but does this level of efficiencyprovide the best protection for those at risk of exposure? Theeffectiveness of the N95 respirator has been supported by asmall study on prevention of occupational transmission of infection.¹However, for work with bacterial bioaerosols and chemical andbiological warfare agents, some have suggested that N95 masksare inappropriate^5,6 because these respirators do not provide"absorbent capability" and because of the amount of mask leakage,which can be about 5% through the filter and 10% around themask,⁷ even if properly fitted. For biological diseases likeSARS, for which just a few particles may be sufficient for infection,the N95 mask may indeed be inadequate, and some health careworkers may therefore become infected even if they use the respiratorproperly. A better selection for respiratory protection would be an N100respirator with an ultra-low penetrating air filter (ULPA),which would cost only slightly more than an N95 respirator.N100 respirators have an efficiency of 99.977%,⁸ and ULPA filtersare 99.999% efficient for monodispersed particles 0.12 �min diameter or larger.⁹ HEPA (high-efficiency particulate air)filters would not be the best selection for use with a respiratorbecause their efficiency is 99.97% for monodispersed particles0.3 �m in diameter or larger, and coronaviruses are smallerthan this (at about 60 to 200 nm). For effective operation ofan N100 respirator with ULPA, the user must be fit-tested. TheUnited States and many other countries have numerous requirementsfor using a negative-pressure air-purifying respirator, includingmedical evaluation and training, as well as yearly fit-testing. John H. Lange Environmental and Occupational Health ConsultantEnvirosafe Training and Consultants, Inc. Pittsburgh, Pa. References 1. Seto WH, Tsang D, Yung RWH, Ching TY, Ng TK, Ho M, et al. Effectiveness of precautions against droplets and contact in prevention of nosocomial transmission of severe acute respiratory syndrome (SARS). Lancet 2003;361:1519-20.[Medline] 2. Schabas R SARS: prudence, not panic [editorial]. CMAJ 2003;168:1232-33. [Free Full Text] 3. Centers for Disease Control. Update: severe acute respiratory syndrome � United States, 2003. MMWR Morbid Mortal Wkly Rep 2003;52: 357-60. [Medline] 4. Martyny J, Glazer CS, Newman LS. Respiratory protection. N Engl J Med2002;347:824-30. [Free Full Text] Sawicki J. Protection from chemical and biological warfare. Surg Serv Manage 1999;5(Sep):11. Available: